Permanent chill mold for the continuous casting of metals

ABSTRACT

A permanent chill mold for the continuous casting of metals. At least one partial region of the outer surface of the permanent chill mold ( 1 ) is provided with cooling channels ( 2, 2   a,    2   b,    2   c ). The depth and/or the width of the cooling channels ( 2, 2   a,    2   b,    2   c ) are greatest in the middle of a sidewall of the permanent chill mold ( 1 ), and they decrease in the direction of the corner region ( 4 ) of the sidewall. Because of this, a uniform heat dissipation can be implemented, and thereby higher casting speeds are possible.

FIELD OF THE INVENTION

The present invention relates to a permanent chill mold for thecontinuous casting of metals.

DESCRIPTION OF RELATED ART

Tube-shaped chill molds made of copper or copper alloys, for castingprofiles made of steel or other metals having a high melting point havebeen described many times in the related art. Permanent chill tubesusually have a uniform wall thickness in a horizontal cross sectionalplane, which increases in the direction of the billet because of theinner conicity of the chill tube. The inner conicity is adapted to thesolidification response of the billet and the continuous castingparameters. Shortly after the setting in of the solidification of thecontinuous casting material, that is, directly below the casting bathlevel, because of the heat transfer that is three-dimensionallycharacteristic over the cross section, there is a greatly differentcharacteristic cooling response. Because particularly great quantitiesof heat are dissipated in the corners of the permanent chill tube, basedon the geometric ratios, that region demonstrates an especially greatstrand shell growth, and therewith an especially great shrinkage. At thesidewalls of the permanent chill tube, the heat dissipation is less, asa rule, although at that location a greater heat flow is imposed at thesame time. The result of the locally different cooling is a non-uniformstrand shell growth, which is able to lead to material stresses andcracks in the strand shell, and thereby increases the risk of a billetbreak-out.

A series of suggestions have been made in the past for achieving ashomogeneous as possible a heat dissipation, and therewith also to createthe prerequisite for a greater casting output. For instance, a permanentchill mold is known from DE 36 21 A1 in which only the arch-shapedsidewalls, but not the corner regions, are provided with coolingchannels. The cooling should, above all, be increased in the region ofthe casting bath level, and this is indeed described in DE 34 11 359 A1.EP 1 468 760 B1 also concerns itself with improvement in the coolingperformance and increase in the casting speed, and the document proposesthat the cooling channels take up 65% to 95% of the outer surface of thecopper tube, the copper tube at the same time being provided with asupporting jacket over the entire circumference and essentially over theentire length. DE 195 81 547 C2 proposes, in the case of verticallyoscillating continuous casting permanent chill molds, to provide theinner surface with recesses or depressions that are situated at aclearance of 15 mm to 200 mm below a casting bath level, as measured ina stable operating state. Stable casting at high speed is also supposedto be made possible thereby. All these attempts do not sufficiently takeinto account the real heat flow distribution.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a permanent chill moldwherein the homogeneity of the billet cooling is able to be increasedeven further, so that as a result one may implement higher castingoutputs and a better billet quality, and which, in addition, contributesto reducing stresses inside the permanent chill mold wall.

This and other objects of the invention are attained by a permanentchill mold for the continuous casting of metals, wherein at least onepartial region of the outer surface (3) of the permanent chill mold isprovided with cooling channels (2, 2 c), and wherein the depth and/orthe width of the cooling channels (2, 2 a, 2 b, 2 c) are greatest in themiddle of a sidewall of the permanent chill mold (1), and they decreasein the direction of the corner regions of the sidewall.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below, using anexemplary embodiment represented in the drawings.

FIG. 1 a is a perspective view of a permanent chill mold 1 which ispositioned in a cooling-water tank that is not shown in detail.

FIG. 1 b is an enlarged perspective view of a portion of the chill moldillustrated in FIG. 1 a.

DETAILED DESCRIPTION OF THE INVENTION

What is important in the permanent chill mold according to the presentinvention is that the cooling effect of the permanent chill mold isoptimized in such a way that it is equivalent to the heat supply of thebillet, so that uniform cooling may be achieved. This is achieved inthat the depth and/or width of the cooling channels are greatest in themiddle of a sidewall of the permanent chill mold, and becomes less inthe direction of the corner regions of the sidewall. What is decisive isthat the cross sectional area of the cooling channels in the middle areaof a sidewall is greater than at the edge region of a sidewall. It hasturned out that, by introducing the cooling channels in the manneraccording to the present invention, the maximum effective stressesoccurring in the sidewall are clearly reduced. Ideally elastic strengthcalculations have confirmed that the effective stress is able to bereduced by more than 30%, from 504 MPa to 348 MPa. This informationrelates to a permanent chill mold cross section of 130×130 mm, a moldtube without channels being compared here to a mold tube designed usingthe channels according to the present invention. The reduction, achievedin this manner, of the stresses in the mold tube has an advantageouseffect on the service life, and reduces the thermally conditioneddistortion of the mold tube. The mold tube, according to the presentinvention, has, in this calculation, eight channels on each sidewall ata clearance of 5 mm, having a length of 200 mm extending in the castingdirection. The middle channels have a depth of 5 mm, whereas the outerchannels have a depth of 4 mm, at a width of 12 mm or 8 mm. There are nochannels situated in the corner regions of the sidewall.

With respect to their depth and width, it is decisive for the specificexecution of the cooling channels that the cooling geometry correspondsas well as possible to the heat flow applied from the inside, andbecause of that, a largely homogeneous temperature field can beachieved, which, up to now, has only succeeded in an unsatisfactorymanner. It is important that the cooling channels be executed deeperand/or wider in the middle of the sidewall, where the heat supply is atits highest, that is, that they have a greater cross sectional area thanin the regions that are close to the corner radii.

Preferably, no cooling channels are provided in the sidewall at adistance of 10 mm to 15 mm from the radius corner region, so as not toincrease the cooling at this position, and not unnecessarily to weakenthe rigidity of the permanent chill mold. The best results may beachieved if the cooling channels have a depth of 3 mm-6 mm. In thiscontext, a residual wall thickness should not fall below 6 mm betweenthe deepest part of the cooling channels and the mold tube interior.

The width of the cooling channels is preferably to be selected between 5mm and 20 mm.

In order to adjust the number of cooling channels to differentformats/dimensions of the mold tubes, it has proven favorable, for thestated channel dimensions, to have a number of 4-10 cooling channels per100 mm of side surface of the mold tube.

Width and depth ratios of the cooling channels between 1 and 4 areregarded as particularly favorable from a flow technology point of view.Ratios deviating from this have unfavorable influences on the flowrelationships, and thus also on the cooling performance as well as therigidity of the mold tube in the region of the bath level. The coolingchannels are provided with a small transition radius to the channelwalls, at the base of the channels, in order to avoid stress peaksthere.

At the run-in region and the run-out region, the cooling channelsideally have a radius which contributes to flow optimization of thecooling water and to the reduction in pressure losses.

In one positioning of the cooling channels regarded as favorable, theirmutual clearance, measured from the middle of the channel, amounts tobetween 10 mm and 25 mm. A ratio of average channel clearance to thewidth of a cooling channel between 1.2 to 3 provides surprisingly goodresults.

Basically, one tries to achieve that the width of the cooling channelsbecomes greater going towards the middle of the sidewall, and inaddition, that the depth also increases going towards the middle. Thedifferent cooling channel geometry is able to be produced either bymetal-cutting processing of the permanent chill mold or even bynon-cutting processing, in reshaping the permanent chill mold.

It is favorable if the cooling channels are situated in a region thatbegins approximately 50 mm above the casting bath level setpointposition and extends to about 300 mm below the casting bath levelsetpoint position, since in this region the greatest heat flow densitiesoccur, and, with that, the stresses in the sidewall of the permanentchill mold are at a maximum. Regions lying lower in the castingdirection, that is, regions at a distance greater than 300 mm below thecasting bath level setpoint position, have also to be cooled, to besure, but, because of the strand shell that has already formed, thetemperature non-homogeneity is not so great that the channels designedaccording to the present invention are absolutely necessary in theselower regions. Superior results are achieved already if the channelsdesigned according to the present invention begin approximately 50 mmabove the casting bath level setpoint position and extend to 300 mmbelow the casting bath level setpoint position.

Chill tube 1 is provided with especially configured cooling channels 2that are formed on the outer surface 3 of the chill tube 1. Coolingchannels 2 do not extend over the entire length of chill tube 1, but arelocated exclusively in the upper, pouring-end region of chill tube 1. Inthis exemplary embodiment, cooling channels 2 have a length of 200 mm.Cooling channels 2 are located in the region of the casting bath levelsetpoint position, the latter lying in the upper one-quarter of coolingchannels 2 shown. The special thing, with regard to cooling channels 2of this chill tube, is that they are not all equally wide and deep, butdiffer in both width and depth. In this exemplary embodiment, coolingchannels 2 a and 2 b, that face corner regions 4, are narrower thancooling channels 2 c that lie in the middle region of the respectivesidewall. Whereas middle cooling channels 2 c, for example, have a widthof 12 mm, the four outer cooling channels 2 a and 2 b may, for instance,have a width of 8 mm. All cooling channels 2 a, 2 b, 2 c are of the samelength. However, not only does the width of cooling channels 2 a, 2 b, 2c vary, but also their depth. This may be seen in that cooling channels2 a, 2 b, 2 c in each case have a radius 5 in the run-in and the run-outregion. The transition of radius 5 to the deepest part of individualcooling channels 2 a, 2 b, 2 c may be recognized by a horizontal line.In middle cooling channels 2 c, the depth is recognizably at itsgreatest. The depth of cooling channels 2 b that are closest together onthe outside is somewhat smaller. In the case of outside cooling channels2 c that face corner regions 4, the depth is the least.

Corner regions 4 are not provided with cooling channels. The chill tubeis fastened in the cooling water tank using a sheet metal waterdeflector, that is not shown in detail, so that the cooling water ispushed into individual cooling channels 2 a, 2 b, 2 c. The sheet metalwater deflectors are positioned in such a way that the chill tube isheld concentrically in the water gap.

1. A permanent chill mold for the continuous casting of metals, thepermanent chill mold having an outer surface (3) which is provided withcooling channels (2, 2 c) in at least one partial region thereof,wherein at least one of the depth and the width of the cooling channels(2, 2 a, 2 b, 2 c) are greatest in the middle of a sidewall of thepermanent chill mold (1), and they decrease in the direction of thecorner regions of the sidewall.
 2. The permanent chill mold as recitedin claim 1 wherein at a clearance of 10 mm to 15 mm from the radius ofthe corner regions (4), no cooling channels (2, 2 a, 2 b, 2 c) aresituated in the sidewall.
 3. The permanent chill mold as recited inclaim 1 wherein the average channel clearance of two cooling channels(2, 2 a, 2 b, 2 c) is in a range of 10 mm to 25 mm.
 4. The permanentchill mold as recited in claim 2 wherein the average channel clearanceof two cooling channels (2, 2 a, 2 b, 2 c) is in a range of 10 mm to 25mm.
 5. The permanent chill mold as recited in claim 1 wherein the ratioof the channel average clearance to the width of a cooling channel (2, 2a, 2 b, 2 c) is in a range of 1.2 through
 3. 6. The permanent chill moldas recited in claim 2 wherein the ratio of the channel average clearanceto the width of a cooling channel (2, 2 a, 2 b, 2 c) is in a range of1.2 through
 3. 7. The permanent chill mold as recited in claim 3 whereinthe ratio of the channel average clearance to the width of a coolingchannel (2, 2 a, 2 b, 2 c) is in a range of 1.2 through
 3. 8. Thepermanent chill mold as recited in claim 1 wherein the ratio of thewidth to the depth of a cooling channel (2, 2 a, 2 b, 2 c) is in a rangeof 1 through
 4. 9. The permanent chill mold as recited in claim 2wherein the ratio of the width to the depth of a cooling channel (2, 2a, 2 b, 2 c) is in a range of 1 through
 4. 10. The permanent chill moldas recited in claim 3 wherein the ratio of the width to the depth of acooling channel (2, 2 a, 2 b, 2 c) is in a range of 1 through
 4. 11. Thepermanent chill mold as recited in claim 1 wherein the cooling channels(2, 2 a, 2 b, 2 c) have a width in a range of 5 mm through 20 mm. 12.The permanent chill mold as recited in claim 2 wherein the coolingchannels (2, 2 a, 2 b, 2 c) have a width in a range of 5 mm through 20mm.
 13. The permanent chill mold as recited in claim 1 wherein thecooling channels (2, 2 a, 2 b, 2 c) are situated in a region whichbegins 50 mm above the casting bath level setpoint position and extendsto 300 mm below the casting bath level setpoint position.
 14. Thepermanent chill mold as recited in claim 2 wherein the cooling channels(2, 2 a, 2 b, 2 c) are situated in a region which begins 50 mm above thecasting bath level setpoint position and extends to 300 mm below thecasting bath level setpoint position.
 15. The permanent chill mold asrecited in claim 1 wherein the cooling channels (2, 2 a, 2 b, 2 c) havea depth of 3 mm to 8 mm at a residual wall thickness, in the region ofthe cooling channels (2, 2 a, 2 b, 2 c), of not less than 6 mm.
 16. Thepermanent chill mold as recited in claim 2 wherein the cooling channels(2, 2 a, 2 b, 2 c) have a depth of 3 mm to 8 mm at a residual wallthickness, in the region of the cooling channels (2, 2 a, 2 b, 2 c), ofnot less than 6 mm.
 17. The permanent chill mold as recited in claim 1wherein four to ten cooling channels (2, 2 a, 2 b, 2 c) are situated per100 mm of chill mold side surface.
 18. The permanent chill mold asrecited in claim 1 wherein the cooling channels (2, 2 a, 2 b, 2 c) areprovided with a transition radius to the channel wall at the channelbase.
 19. The permanent chill mold as recited in claim 1 wherein thecooling channels (2, 2 a, 2 b, 2 c) have a radius (5) in their run-inand their run-out regions